1. Field of the Invention
The invention relates generally to the construction of electric motors, and more particularly to systems and methods for constructing ferromagnetic laminations that are used to build the cores of electric motors, where the laminations are constructed using powder metallurgy techniques.
2. Related Art
A typical electric motor has two primary components: a rotor; and a stator. The stator remains stationary, while the rotor rotates with respect to the stator. In an AC induction motor, magnetic fields generated by the stator induce currents in the rotor. These currents in turn generate magnetic fields that interact with those of the stator. The interaction of the magnetic fields created by the stator and the rotor cause the rotor to rotate with respect to the stator.
Induction motors are commonly used in downhole motors that drive electric submersible pumps (ESP's). Typically, the stator of an ESP motor is constructed by positioning coils (windings) of insulated wire in slots in a ferromagnetic stator core. When electric current is passed through the wire, magnetic fields are generated around the wire and consequently in the ferromagnetic stator core. Changing the magnitude and direction of the current changes the magnitude and polarity of the magnetic fields generated by the stator.
AC electric motors, including motors that are used to drive ESP's, commonly include a stator core that is manufactured using ferromagnetic laminations. The laminations are electrically insulated from each other in order to prevent currents (known as eddy currents) from circulating through the stator core. These currents reduce the efficiency of the motor and increase the heat generated in the motor.
The laminations are typically stamped from thin sheets of metal. The particular metal that is used is selected based in part on its magnetic and thermal properties. Ideally, the metal would have high magnetic permeability and high thermal conductivity, but in practice, it is often necessary to select a metal that has a balance of these properties. In other words, it may be desirable to select a metal that has moderate magnetic permeability and thermal conductivity, rather than one that has a very high magnetic permeability but a low thermal conductivity (or one that has a high thermal conductivity but a low magnetic permeability).
It would be desirable to provide means to allow a designer of a downhole motor to have the best of both worlds—the high magnetic permeability of one metal and the high thermal conductivity of a different metal.